Conventionally, a Ni-plated steel sheet has been popularly used as a material for manufacturing battery cans. Also, to further enhance the corrosion resistance of an outer surface of a battery can, there has been used a Ni-plated steel sheet where Ni plating is formed on a surface of a steel sheet corresponding to an outer surface of a battery can and, thereafter, a Fe—Ni diffusion layer is formed by applying heat treatment to the Ni-plated steel sheet.
As properties which such a Ni-plated steel sheet for manufacturing a battery can is required to possess, the stable press formability can be named along with the excellent battery characteristic and the excellent corrosion resistance. The stable press formability means that the scratches are not formed on a battery can and no seizure is generated at the time of press forming. Press formability is an important factor in terms of productivity for preventing a press machine from being shut down because of maintenance done on a mold.
Further, in terms of environment, there has been a demand for the reduction of the environmental load by using a non-organic solvent and non-alkali cleaning where cleaning after pressing is performed using an aqueous solution containing a surface active agent.
Accordingly, there has been a demand for a Ni-plated steel sheet which enables the manufacture of a battery can by press forming even when a water-based emulsion or a press liquid of low viscosity is used.
For example, patent document 1 (Japanese Patent 4051012) discloses a Ni-plated steel sheet for a battery can where a Fe—Ni diffusion layer or a Fe—Ni diffusion layer and a recrystallized softened Ni-plated layer which is formed on the Fe—Ni diffusion layer are formed on a surface of a steel sheet corresponding to an outer surface of the battery can, and a Ni-plated layer containing a brightening agent or a semi-brightening agent is formed on the above-mentioned layer, and an average surface roughness Ra of the Ni-plated layer is set to 0.3 μm or more. Also in such a Ni-plated steel sheet, a coating weight of the Fe—Ni diffusion layer or a coating weight of the Fe—Ni diffusion layer and the recrystallized softened Ni-plated layer formed on the Fe—Ni diffusion layer is 5 to 45 g/m2 in terms of Ni (a Ni amount of the Fe—Ni diffusion layer or a total Ni amount of the Fe—Ni diffusion layer and the recrystallized softened Ni-plated layer formed on the Fe—Ni diffusion layer), and a coating weight of the Ni-plated layer containing the brightening agent or the semi-brightening agent is, in terms of Ni, 0.5 g/m2 or more and less than an Ni amount of a layer below the Ni-plated layer (the Ni amount of the Fe—Ni diffusion layer or the total Ni amount of the Fe—Ni diffusion layer and the recrystallized softened Ni-plated layer formed on the Fe—Ni diffusion layer).
Further, patent document 2 (Japanese Patent 4051021) discloses a Ni-plated steel sheet for a battery can where an Fe—Ni diffusion layer is formed on a surface of a steel sheet corresponding to an outer surface of the battery can, and a Ni-plated layer containing a brightening agent or a semi-brightening agent is formed on the Fe—Ni diffusion layer, average roughness Ra of the Ni-plated layer is 0.1 μm or more and 1 μm or less, and its Rmax is 1 μm or more and 10 μm or less. Also in such a Ni-plated steel sheet, a coating weight of the Fe—Ni diffusion layer is 5 to 45 g/m2 in terms of Ni and a coating weight of the Ni-plated layer containing the brightening agent or the semi-brightening agent is 0.5 to 20 g/m2 in terms of Ni.